ABSTRACT: Using framework monoclonal antibodies (mAb) against the T cell receptor (TCR) alpha beta complex, we found that not all T cells in human peripheral blood were TCR alpha beta+. A population of TCR alpha beta- CD3+ cells was found to express a second T cell receptor composed of CD3, the protein product of the rearranging T gamma gene, and an incompletely characterized TCR delta subunit. This receptor is expressed on the surface of a novel population of human and murine peripheral blood T cells and occurs in specific forms based on the TCR gamma polypeptide size, C gamma I or C gamma 2 gene segment usage, and the presence or absence of disulfide linkage. We wish to elucidate the structure of the TCR gamma and delta proteins and genes. In particular, we will determine the peptide backbone size, number and type of carbohydrates, presence of variability in peptide maps and determined partial amino acid sequence for the TCR delta chain. We propose to clone the gene for this subunit by oligonucleotide hybridization (based on determined amino acid sequence) or by lambda gt11 expression screening (with specific anti-TCR delta sera) or by cross-hybridization with the murine X gene (Y-h Chien and M Davis). The deduced structure of cloned genes will be compared to the determined biochemical features and sequence obtained from purified TCR delta protein to establish the identity of the cloned genes. To study the function of TCR gamma delta lymphocytes, various stimulating antigens will be used in efforts to define the specificity (and possible MHC restriction) of these cells. In addition, their demonstrated ability to kill malignant cells (natural killer-like activity) will be investigated to determine if the TCR gamma delta recognizes tumor-specific antigens. The cloned TCR gamma and delta genes will then be transfected and expressed in order to determine the rules which govern pairing of the different TCR gamma and delta forms, and to reconstitute a functional receptor. The ultimate goal is to understand what functional role this new population of T cells plays in the immune system.